It reminds me very much of a Tojeiro we had as a puzzle a few years ago - I have tried every variation possible using our search, but that puzzle will not surface.
It's also very similar to bodies made by Dawes & Offord for Buckler chassis. Having said all that, this is obviously a GRP creation. Is this a shell which was available in the 1950s/60s and is now being remade from the old moulds under another name?